Difference between revisions of "PChem312 s22 w11"
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:1) Use the heats of formation to determine the ΔH<sub>rxn</sub> for the 3 reactions discussed yesterday. | :1) Use the heats of formation to determine the ΔH<sub>rxn</sub> for the 3 reactions discussed yesterday. | ||
:2) make a table (by hand or Excel) | :2) make a table (by hand or Excel) | ||
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| − | |ΔHrxn - experimental||ΔHrxn - heats of formation | + | ! ||ΔHrxn - experimental||ΔHrxn - heats of formation |
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==Friday, March 25th== | ==Friday, March 25th== | ||
| − | + | In-person meeting...See you at 9 am. | |
Latest revision as of 12:13, 25 March 2022
Welcome to a week of online PChem! As you know, 11 MC students, faculty and staff are attending the 258th bi-annual ACS meeting in San Diego, CA...YES there have been 257 previous ACS meetings (2 per year). At this years meeting there are ~11,500 abstracts/presentations, ~9,000 in-person attendees, and another ~3,000 virtual registrants.
So, in my absences, i ask you to complete the following work. On Monday March 28th, you will bring to class all of the completed work listed below in a form that can be turned in, ie. hard copies.
Monday, March 21st
Worksheets from Friday...
- Worksheet 1: Fuel Worksheet
- Worksheet 2: Thermite Worksheet
New worksheet...
- Worksheet 3: Home Heating
Tuesday, March 22nd
Welcome to an online PChem lab activity. This is a standard calorimetry lab where we determine the ΔHrxn for three related, but different reactions. We have done previously in gen chem, but replaced it with the burning of food stuff because setting Cheetos on fire is much more exciting...now you get to do the more boring lab now.
If we were doing this in the lab, you would collect temperature vs time data for a set of three reactions:
- NaOH (s) --> NaOH (aq)
- NaOH (s) + HCl (aq) --> NaCl (aq) + H2O (l)
- NaOH (aq) + HCl (aq) --> NaCl (aq) + H2O (l)
The data would look like this (collected by A. Trenttin - Fall 2020):
These reactions are done in a "coffee cup calorimeter" and although the insulating properties of the cups is not great (notice the temperature drops after reaching a max), we can compensate for this by carrying out the Tf analysis shown on the graph. By fitting the data to identify the rate of heat loss, we can determine the Tf values indicated on the graph.
Additional Data
Reaction 1 - data
- NaOH (s) --> NaOH (aq)
- - 100 mL of DI H2O
- - 3.51 g NaOH --> (40.00 g/mol) --> 0.0878 moles NaOH (s)
- - ΔT = 34.4 - 22.0 = 12.4 oC
Reaction 2 - data
- NaOH (s) + HCl (aq) --> NaCl (aq) + H2O (l)
- - 100 mL of 1.00 M HCl (aq)
- - 3.43 g NaOH --> (40.00 g/mol) --> 0.0856 moles NaOH (s)
- - ΔT = 35.8 - 22.0 = 13.8 oC
Reaction 3 - data
- NaOH (aq) + HCl (aq) --> NaCl (aq) + H2O (l)
- - 50.0 mL of 1.00 M HCl (aq)
- - 50.0 mL of NaOH (aq) containing previously dissolved 1.76 g NaOH --> (40.00 g/mol) --> 0.0440 moles NaOH (s)
- - ΔT = 23.9 - 22.0 = 1.9 oC
Use the data above to calculate the ΔHrxn for all three reactions. - So where do you start?
- First determine how much heat was generated from the reaction by using the standard q = mass * sp heat * ΔT.
- Second, this heat was generated from a specific amount (moles) of NaOH...q/mole NaOH = ΔHrxn...repeat for all three.
- Please show all of your work...Done.
Wednesday, March 23rd
- 1) Use the heats of formation to determine the ΔHrxn for the 3 reactions discussed yesterday.
- 2) make a table (by hand or Excel)
| ΔHrxn - experimental | ΔHrxn - heats of formation | |
|---|---|---|
| Rxn 1 | ||
| Rxn 2 | ||
| Rxn 3 |
Read the section in your Textbook about Hess' Law. Use the three reactions discussed yesterday to show how Hess' Law applies to this data.
Friday, March 25th
In-person meeting...See you at 9 am.